I've never had this problem. Did you try deleting the wifi profile and recreating it? Are you using an older router?

Yeah, I've tried deleting and re-creating all of the profiles. It's happening on every network I connect to - hotspot from 9930, connectify from laptop, cisco aeronet's @ home and work & a linksys wrt that I use for 'testing'. None are N devices, and are are running the most current firmware. I'm also using AES instead of TKIP where possible. I'm starting to think it may getting confused when there are multiple saved networks available and is switching between them to a point where it gets so confused that I can't connect to anything unless I turn wifi off & back on. I'm going to try disabling/deleting all but one saved network and see if the situation improves.

Well, I can confirm that the issue is related to having saved profiles for multiple networks that are available at the same time. When I keep all off the WiFi profiles (except for the one I want to use) disabled, the WiFi is stable (tested on 6 different networks). As soon as a second (or more) saved profile is marked active, and the Playbook gets within range of 2+ saved networks, it starts switching between them every 30 seconds or so. After 4-5 minutes of this, I can't connect to any network until I disable wifi & re-enable it.

I can deal with the workaround of having to manually enable/disable wifi profiles as needed, but would prefer not to. If anyone finds a solution (or better workaround) I'd love to know.